random freezes; ram or mobo?

[SimJoe]

I started to have this weird problem where my pc would totally lock up and freeze whenever i play games and movies a week or so ago. The weird thing is, my pc will only freeze if i'm playing a game or a movie. Normal putzing around (web, email, chatting, that sort of jazz) works perfectly fine and nothing bad happens.
For some reason, I doubt it's a software problem (at least I hope it isn't)... so I started to test components in my pc. I know it's not the CPU because it happened two or three times before I popped in my new chip (1600+ -> 2000+). It's not my tv tuner card or NIC. I wasn't able to test video sinice I don't have any spare video cards laying around.

So then I went straight to some ram tests (with memtest86) and BAM! errors occured on two tests (test 5 and 8). All the errors were on the same pattern and on both sticks of ram.
Since it was on both sticks of ram, some failure on both, and very repeatable.. i thought.. hey, maybe it's my ram. But then when i borrowed some ram from a friend and tested it in my pc, the SAME thing happened. then when i tested his ram in his computer, they passed the test and worked perfectly fine.
So now i'm thinking it might be my motherboard that's causing the problem...

hmmm.. yeah, that was a lot of ranting and rambling, let me summarize
pc freezes on games and videos
checked cpu, nic, and tv tuner card
tested ram (failed on tests 5 and 8 on one pattern)
tested friend's ram (failed on tests 5 and 8 on the same one pattern)
tested friend's ram in their pc.. passed with flying colors

soo.. tomorrow i'm going back to school.. and can finally test my ram in another friend's pc. other than that, is there anything else i should do? I'm about 90% sure it's a mobo problem, but there could be something i'm overlooking.
help?

 

[synoptism]

Did you change anything in relation to hardware and/or software before you started having this problem?

Why do you doubt it's a software problem? If something comes up "out of the blue" then I usually instinctively think to check everything on my hard drive. Just for kicks, try a virus and adware scan. Just to methodically check things one-by-one so you eliminate it out of the equation.

 

[plot]

1. mobo
2. PSU is dieing (not enough power for vid games... causes system reboots and lockups)
3. heating problem. check your cpu and case temps

 

[SimJoe]

nothing was changed or touched before this started to happen.
it's probably not overheating either (running 36c/33c under full load).
It could be windows, but i'd rather not just randomly reformat it if i don't have to yet.
I've done virus/adware scans already and nothing turned up.

yeah, kinda rambling but i just woke up >_<
umm.. I still have to test my ram, but other than that, any other ideas?

edit:
oh yeah, i'm not sure if this is any indication that my psu is fine.. but..
2.5v = 2.73
3.3v = 3.57
5v = 5.10
12v = 12.07